1. Field of the Invention
The present invention relates to a photoelectric conversion apparatus used in a facsimile system, an image scanner, or the like.
2. Related Background Art
In recent years, an elongated line sensor including an optical system having a 1:1 magnification has been developed as a photoelectric conversion apparatus for a compact, high-performance system such as a facsimile system and an image reader. In a conventional line sensor of this type, signal processing ICs (Integrated Circuits) constituted by switching elements or the like are connected to photoelectric conversion elements arranged in an array, column-wise. However, the number of photoelectric conversion elements is 1728 is required for an A4 size when the photolectric conversion apparatus complies with the facsimile G3 standard. A large number of signal processing ICs are therefore required. For this reason, the number of mounting steps is increased, the manufacturing cost is increased, and sensor reliability is degraded. A matrix wiring pattern is employed to reduce the numbers of signal processing ICs and mounting steps.
FIG. 1 is an illustrative block diagram of a photoelectric conversion apparatus employing matrix wiring. Referring to FIG. 1, the photoelectric conversion apparatus includes a photoelectric conversion unit 31, a scanning unit 32, a signal processing unit 33, and a matrix wiring unit 34.
The apparatus further includes individual electrode wirings 35 and common electrode wirings 36.
In the photoelectric conversion apparatus having the above arrangement in FIG. 1, since a wiring of the common electrodes 36 runs along a longitudinal direction of a sensor substrate, a large electrostatic capacitance is present between the electrodes. For this reason, signal crosstalk undesirably occurs. In order to eliminate the above disadvantages, in a conventional photoelectric conversion apparatus, separating electrodes 37 are arranged between the common electrodes so as to reduce the electrostatic capacitance between the common electrodes and prevent signal crosstalk, as shown in FIG. 2.
Note that each hollow dot in FIG. 2 represents an intersection 38 between the corresponding separating electrode wirings and individual electrode wirings. FIG. 3 is an enlarged view of the matrix wiring unit in FIG. 2. The matrix wiring unit includes contact holes 39 for respectively connecting the separating electrodes to the common electrodes.
In the photoelectric conversion apparatus in FIG. 2, though signal crosstalk between the common electrodes can be prevented, signal variations undesirably occur.
More specifically, as shown in FIG. 2 the numbers of intersections 38 between the individual electrode wirings and separating electrode wirings vary in the individual electrodes. Since the electrostatic capacitance between the common electrode wirings 36 and ground 40 varies upon a wiring, large signal output variations occur. In order to solve the above problems, even if a correction capacitor is connected to each common electrode wiring 36, it is difficult to completely prevent signal output variations of each photoelectric conversion element because of nonuniformity of thickness distribution of insulating layers.